Section 5 - Solid-fuel heating systems

This section provides guidance on the specification of solid-fuel heating systems for dwellings.

5.1 - Scope of guidance

The guidance given in this section covers the following types of solid-fuel heating appliances and systems used to deliver primary and secondary heating:

Batch-fed open fires.
Batch-fed and automatic-feed dry room-heaters/stoves.
Batch-fed log and multi-fuel appliances.
Automatic-feed pellet stoves.
Batch-fed and automatic-feed room-heaters with boilers.
Batch-fed cookers with boilers not exceeding 7.5kW.
Batch-fed independent boilers and automatic-feed anthracite and wood-pellet independent boilers.
Central heating systems using certain types of solid-fuel appliances.

Where appropriate, it may also be necessary to refer to the sections of this guide on community heating, underfloor heating, solar water heating and micro-CHP.

5.2 Solid-fuel appliances for primary heating

Solid-fuel appliances that are provided in new and existing dwellings for primary heating should have a minimum efficiency (gross calorific value) no less than that specified in Table 16 for that category of appliance.

Table 16

Table 16A

Supplementary information on solid fuel appliances

Minimum efficiencies

Individual manufacturer’s efficiency figures may be higher than those indicated and should be used where independently certified against the harmonised European Standards now in place.

Carbon emission factors

Solid fuels include various forms of woods, coals, and manufactured solid fuels and, consequently, there is a range of associated CO~2~ emission factors. CO~2~ emission factors are as important as appliance efficiency when selecting a boiler. Table 17 shows the CO~2~ emission factors for generic types of solid fuel recognised in DEAP (see also table 8 in the DEAP manual)

Some appliances can only burn a single type of fuel while others may be able to burn a range of types. The ‘multi-fuel’ category in Table 17 allows for the latter group, basing its CO~2~ emissions on a typical blend of fuels used in that case.

Smoke control areas

Wood should always be seasoned to a moisture content not exceeding 20% to ensure maximum performance and limit the occurrence of condensation and deposits in the chimney system.

All solid-fuel appliances require appropriate soot-fire resistant chimneys discharging at high-level locations defined within J (TGD-J) 2014.

Table 17

Table 17A

5.3 - Central heating systems using certain types of solid-fuel

This section provides guidance on the specification of fixed solid-fuel heating systems for dwellings. The guidance covers the following types of solid-fuel appliances used to deliver primary heating as part of a central heating system:

Batch-fed open fires with high-output boilers (appliance types D1–D4 in Table 16).
Batch-fed and automatic-feed room heaters and stoves with boilers (appliance type F in Table 16).
Batch-fed cookers with boilers not exceeding 7.5kW (appliance types G1 and G2 in Table 16).
Batch-fed independent boilers and automatic-feed anthracite and wood-pellet independent boilers (appliance types J1–J5 in Table 16).

Unless otherwise stated, the guidance in this section applies equally to appliances that burn wood, wood pellets, house coal, manufactured smokeless fuels and anthracite. Where appropriate, it will also be necessary to refer to the sections on community heating, underfloor heating, solar water heating and micro-CHP.

Terminology and applicability of guidance to different scenarios in new and existing dwellings

The guidance in this section applies to the following situations:

The specification of central heating systems in new dwellings – this situation is referred to in this section as a new system.
The specification of central heating systems in existing dwellings where previously space heating was not provided by central heating – this situation is also referred to in this section as a new system.
The specification of a replacement central heating system and/or component in existing dwellings where central heating is already installed – this situation is referred to in this section as a replacement system.

In situations (a) and (b) above the guidance for compliance of new systems (in new and existing dwellings) with Part L is the same.

In situation (c) above, that is for replacement systems in existing dwellings, in most cases the guidance for compliance with Part L is as for new systems, unless otherwise stated in the relevant section.

In order to comply with the requirements of Part L 2008, a central heating system using a solid-fuel appliance which is provided as a new system or replacement system in dwellings should meet all of the following conditions:

The appliance should be from the categories D, F, G and J as defined in Table 16.

AND

The appliance should have a minimum efficiency (gross calorific value) of no less than that specified in Table 16 for that category of appliance

AND

The installer should confirm that the ratio of heat to room and heat to water is appropriate for the room and total property. This will require reference to installation practice guidelines including calculation of room and property heat loss.

AND

The minimum provisions for system circulation as given in Table 18 (row a) need to be met.

AND

the minimum provisions for fuel storage should be met as given in Table 18 (row b).

AND

The minimum provisions for hot water storage and labelling of storage vessels as given in Table 18 (row c) need to be met

AND

The minimum provisions for system preparation and water treatment as given in Table 18 (row d) should be met.

AND

The system should be commissioned in accordance with the minimum provisions given in Table 18 (row e).

AND

The minimum provisions for control of the heating and hot water circuits, as given in Table 19 should be met. An acceptable alternative to these is any boiler management control system that meets the specified zoning, timing and temperature requirements.

AND

Pipework should be insulated as described in Table 20

Supplementary information

Turn-down values (i.e. the ratio of high to low output)

Turn-down ratios are generally very good (>10:1) for automatic-feed appliances with small firebeds.
Turn-down ratios are less good with large batch-fed appliances unless these are used in conjunction with a hot water accumulator.
Automatic appliances are likely to require less frequent refuelling. Automatic (e.g. electric or gas) ignition is now available for certain designs and reduces energy usage at times of low demand, allowing boiler interlock.
Some boilers have both auto-ignition and fire-extinguishing features.

Link-up systems

It is possible to connect together two or more heating appliances with boilers (at least one of which can be solid-fuel fired), to maximise flexibility and efficiency. For example, an oil or gas boiler could be combined with a wood-burning stove with boiler sited in the living room. This combination with wood burning appliances will reduce overall carbon emissions. Both systems should be designed to appropriate installation codes.

Controls for solid-fuel central heating

Boiler interlock, provided by a wiring arrangement, to prevent the system from operating when there is no demand for heat, should only be fitted if recommended by the manufacturer.
In some simple batch-fed or automatic appliances (without heat stores and/or without automatic ignition) it is not possible to switch off the heat output completely, however the appliance output can be lowered to a minimum to reduce fuel consumption.
In most solid-fuel systems the room thermostat will switch off the pump, which in turn will cause the boiler to operate at minimum output.
Some automatic solid-fuel systems can be fitted with weather compensation, and incorporate multi-zone control. It is important to seek guidance from the manufacturer, especially if the heating package is to include other fuels.

Table 18

Tables 18A & B

Table 19

Table 19A

Table 20

Table 20A

5.4 - Solid-fuel appliances for secondary heating

Solid-fuel appliances in new and existing dwellings, which are provided for secondary heating and are not part of a central heating system, should have a minimum efficiency (gross calorific value) no less than specified in Table 16 for that category of appliance.

Supplementary information – solid-fuel appliances providing secondary heating

Boiler interlock, provided by a wiring arrangement, to prevent the system from operating when there is no demand for heat, should only be fitted if recommended by the manufacturer.
In some simple batch-fed or automatic appliances (without heat stores and/or without automatic ignition) it is not possible to switch off the heat output completely, however the appliance output can be lowered to a minimum to reduce fuel consumption.
In most solid-fuel systems the room thermostat will switch off the pump, which in turn will cause the boiler to operate at minimum output.
Some automatic solid-fuel systems can be fitted with weather compensation, and incorporate multi-zone control. It is important to seek guidance from the manufacturer, especially if the heating package is to include other fuels.
Controls may be provided by any boiler management control system that meets the specified zoning, timing and temperature, and boiler interlock control requirements.
The level of sophistication should generally be appropriate to and compatible with the appliance. The highest levels are only appropriate to appliances with automatic ignition.
As far as it is practicable to do so when working on existing systems, controls should be upgraded to the levels defined for new systems.

Table 20

5.4 Solid-fuel appliances for secondary heating

Solid-fuel appliances in new and existing dwellings, which are provided for secondary heating and are not part of a central heating system, should have a minimum efficiency (gross calorific value) no less than specified in Table 16 for that category of appliance.

Supplementary information – solid-fuel appliances providing secondary heating

Minimum efficiencies

Individual manufacturer’s efficiency figures may be higher than those indicated in table 16 and should be used where independently certified against the harmonised European Standards now in place.

Appliance types

Appliances which are most suitable for secondary space heating are summarised on the following page.

5. Solid-fuel heating systems